1. Field of the Invention
The invention generally relates to the conversion of solar energy into forms suitable for substantially unattenuated transfer through the earth's atmosphere for use in performing useful work, for instance, at the earth's surface or elsewhere, and more particularly concerns a stabilized photochemical laser satellite device for the conversion of solar energy directly into laser energy in the form of a relatively narrow wave length band of electromagnetic energy used remotely for electrical power generation or the like after passage through the earth's atmosphere, for example.
2. Description of the Prior Art
It is readily recognized that a vast quantity of solar energy is received daily upon the earth's surface and by its atmosphere and is daily re-radiated into space and lost, a quantity quite sufficient to supply many present and future needs for electrical and other power. Direct heating and cooling of individual buildings have long been successfully achieved by circulating fluids through solar energy collectors, then storing the heat for later use. Mirrors have been used at the earth's surface to track the sun and to concentrate the solar flux into a receiver at the earth's surface to generate steam for driving electrical generators.
Photovoltaic arrays at the earth's surface have produced electricity from the sun's rays by a non-thermal process. Natural collection of solar energy takes place on and near the earth's land and ocean surfaces and may be exploited by extracting energy from accumulated rainfall, or from the wind or tides. One important conversion mechanism is bioconversion, whereby growing plants store solar energy that is later released directly by burning the plant or, for example, by its chemical conversion to a fuel such as an alcohol.
Solar energy is not free, any more so than is power from other convertible resources; the initial cost of any mechanism for its mass conversion into electrical or other energy of form suitable for distribution by present or future distribution systems is considerable. Of greater significance is the fact that the solar energy received at the earth's surface is highly variable. The time of day (or night), the season of the year, and scattering or attenuation of solar energy due to weather conditions, all seriously affect the magnitude of solar flux intercepting any area of the earth. However, the solar radiation impinging upon a surface of standard area normal to the sun's rays and disposed above the earth's atmosphere is found to be large and substantially constant.
The problem of efficient conversion of solar radiation into useful electrical or other power has stimulated the publication of several untried suggestions, some radical indeed. Of these suggestions, one which has apparently been given serious consideration was fostered in the article "Solar Power From Satellites" appearing as a release of Arthur D. Little, Inc., in the Feb. 1977 issue of Physics Today, pages 30 through 38. So as to enjoy the use of the greater magnitude, more nearly constant solar flux densities available above the earth's atmosphere, it was proposed to assemble in space above the earth's atmosphere enormous arrays of photovoltaic cells held together by a frame having dimensions about 5 by 13 kilometers. The photovoltaic cells would generate sufficient electrical energy to power an array of synchronized microwave generators coupled to a directionally controlled microwave radiating antenna for directing a microwave beam to a receiving antenna positioned at the end of the line of sight, as at the earth's surface. The microwave energy thus arriving at the earth's surface is not in suitable form for direct use and must be converted to more conventional form if it is to be generally distributed. Furthermore, the several microwave oscillators must be frequency and phase synchronized by complex control means.
Essentially, the prior art proposal requires a double conversion process; a narrow band of the solar energy is first converted to high voltage electricity (20 k.v.d.c.) by the solar cell array and the microwave oscillators then convert the high voltage energy to microwave energy. Solar cells having efficiencies of 15 percent have been reported, but experience shows that this value is rarely met and seriously decreases with each year of use. Microwave generators are also relatively inefficient devices and reach reasonably good efficiencies only by the use of heavy devices for producing permanent magnet or solenoid focussed electron beams. Many other factors tend to decrease system efficiency, and overall efficiency of the proposed system does not appear to be attractive in view of the enormous total mass and cost of construction and operation of the system.
For example, it is estimated that the aforementioned approximately 5 by 13 kilometer solar cell array and its associated microwave and control equipment would be transported piece by piece from the earth to be assembled in space. Further, the operating power station would clearly need maintenance during its operating life and the costs of both of these operations are significant in determining the economic feasibility of the concept. Operating costs alone of the huge structure (18.2.times.10.sup.6 kg), not including consumables, is significant; the energy cost alone of stabilizing the giant platform can be enormous. Most discouraging is the fact that the vast scope of the structure does not lend itself to a reasonably uncomplex test of a model of size conveniently put into space by a single rocket.